Mozilla said the upgrade should result in "added performance for applications and games." Don't be surprised, though, if certain sites requiring plugins that worked in previous 32-bit versions don't work in Firefox 64-bit for Windows.

In October, Mozilla announced plans to end support for the aging Netscape Plugin Application Programming Interface (NPAPI) by the end of 2016. Once essential to the Web experience, NPAPI has been replaced by streaming video, advanced graphics, and gaming features.

Introduced in early November, the Windows, Mac, Android, and Linux-based program prevents sites from gathering data about your Web activity. While browsing in a private window, it blocks ads, analytics trackers, social share buttons, and other content that may record behavior without your knowledge.

If that's not enough, though, choose a "strict" protection block list, which will stop additional trackers—like those found in video, photos, and embeddable content.

There is a catch, though: Choosing that list could mean some sites do not operate properly, or at all.

Last month, Firefox hit iOS devices worldwide, letting you surf the Web on an iPhone, iPad, or iPod touch. Similarly, the Firefox OS Developer Preview is available now without having to flash it as your primary operating system.